In a copending U.S. patent application filed in the names of Michael F. Wicnienski and Donald E. Charles, entitled "Dosimeter For Photometric Applications", Ser. No. 389,430, filed June 17, 1982, there is disclosed a dosimeter which could be used in a germicidal chamber, for determining the amount of ultraviolet irradiation that has been received. The dosimeter disclosed in the aforementioned patent application includes a voltage or current to frequency converter which provides having a frequency that is proportional to the amplitude of the input voltage or current. If the voltage or current to frequency converter happens to fail in a manner such as to generate an abnormally high output frequency, the dosimeter could perceive that the dose of irradiation has occurred although there has actually been provided an unsafe, foreshortened dose. Thus when using a dosimeter which incorporates a voltage or current to frequency converted it is important that an abnormally high output frequency of the converter be detected.
There are other systems which depend upon the counting of output pulses from a voltage or current to frequency converter. If such output pulses have a frequency that is below a certain threshold or a frequency that is above a certain threshold, the system may not operate properly and a dangerous condition may be presented. In such systems, it is important that abnormal frequency variations be detected